The overall objective of the proposed research is to elucidate in molecular terms the mechanism by which interferon acts to affect a wide variety of fundamental viral and cellular processes. The specific aims are: (1) to purify the apparent interferon-mediated ribosome -associated polypeptide present in interferon-treated mouse ascites and fibroblast cells and normally absent in untreated cells, and then to determine the biochemical properties of the purified polypeptide; (2) to elucidate the precise biochemical step in the translation of viral messenger RNA in vitro that is inhibited in cell-free systems from interferon-treated cells but not in systems prepared from untreated cells; (3) to resolve whether the inhibitory activity of the host-coded interferon-mediated factor is directed specifically toward viral messenger RNAs, or whether the translation of certain classes of cellular mRNAs are also selectively affected; (4) to determine the species-specificity of the host-coded interferon-mediated inhibitor of messenger RNA translation in vitro. BIBLIOGRAPHIC REFERENCES: Davies, J. W., and Samuel, C. E. (1975) Translation of Virus mRNA: Comparison of Reovirus and Brome Mosaic Virus single-stranded mRNAs in a Wheat Germ cell-free system. Biochem. Biophys. Res. Commun. 65: 788-796.